CAR or TRUCK discharges while driving down highway

WARNING NEW CAR AND TRUCK OWNERS: Most these vehicles have what is called a Smart Alternator (actually, needs new design). When traveling for some distance on the highway the computer will switch off the alternator and the battery will begin to slowly discharge (lights and all on) and this is used to save torque on engine and thus some gasoline. Look close, on your volt meter and you should see a RED DOT that this discharge "should not" go below. If it by chance it does, then pull over stop, count to 10, restart car/truck and keep fingers crossed. Again, I think the system should "trickle charge" if nothing else.

I dont think the dealer knew what he was doing ,your altenator has 6 diodes inside it and the are a one way check valve for current,If one fails no light will come on because it is still charging,But will drain your battery,I hope this helps you and have a merry x mas and please dont forget to vote on this solution

Could be as simple as adjustment if no air conditioning on vehicle. Little more work if it does have A/C. Worse case scenario, it's not the belt but alternator/generator. Check belt condition & tension & go from there.